Answer:

Entity: Programmer

Attributes:

Programmer_code(Primary Key), Log-in_Name (Foreign Key)

Entity2, Program

Attributes:

Program_name(Primary key), Extension, Programmer_code (Foreign Key)

Version_Number, Date, Description. 

Entity3: User

Attributes:

Log-in_Name(Primary Key). 

Relationships: 

This database has three major entities which are users, programmers, and programs. The programmers are the developers of the programs and determine which users are allowed to use a program. A program is written and customized by one programmer and two or more programs can call each other. Each program is developed by one programmer too. Such relationships are very useful in the database because they specify which roles an entity plays in the database and which privileges it enjoys in the database too. They were designed to regulate the interactions and flow of data in the database. Since the database design, the primary key plays an important role in storing and retrieving the data, here for all the tables, the primary key is defined which uniquely identified the row of the database. So, A primary key is the column or columns that contain values that uniquely identify each row in a table.

For all the defined entities the primary key attribute is defined, for the programmer column name  programmer_code is defined as a primary key. While program entity has the

Program_name(Primary key) and User has a Log-in_Name(Primary Key). If we want to perform the joining operation with the two entities then we need to have the foreign key in the table, so if we want to join the three tables then first we can join the entity User and Programmer using the

Log-in_Name column, and then we can join the program table with the merged entity using the

Programmer_code attribute. So likewise we can join all the different three table entities using the foreign key concepts and retrieve the data from the tables.